Liquid heating feedback system

ABSTRACT

A liquid heating feedback system for elevating the temperature above the dew point of the liquid feed to a heat exchanger of a liquid heating system, particularly of the &#39;&#39;&#39;&#39;once-through&#39;&#39;&#39;&#39; type wherein the liquid feed is not recirculated through the heat exchanger. A Venturi injector is employed to permit the feedback of a portion of the heated liquid from the heat exchanger to be commingled with the liquid feed being pumped to the heat exchanger. By preheating the liquid feed up to the dew point prior to being fed into the heat exchanger, the formation of condensate on the surfaces of the heat exchanger can be practically eliminated, thereby extending the useful life of the heat exchanger, burner and associated combustion components.

United States Patent 1 Mulholland et al. I I

[ 5] June 4, 1974 LIQUID HEATING FEEDBACK SYSTEM UNITED STATES PATENTS6/1928 Clay..,.. 239/136 9/1942 Malsbary et al. 239/137 5/1953 Hull 1239/137 Arant 239/137 64.: VALVE Yam: H055 6313 (cad/mm) PrimaryExaminer-Lloyd L. King Attorney, Agent, or FirmCar0thers and Carothers[5 7] ABSTRACT A liquid heating feedback system for elevating thetemperature above the dew point of the liquid feed to a heat exchangerof a liquid heating system, particularly of the once-through" typewherein the liquid feed is not recirculated through the heat exchanger.A Venturi injector is employed to permit the feedback of a portion ofthe heated liquid from the heat exchanger to be commingled with theliquid feed being pumped to the heat exchanger. By preheating the liquidfeed up to the dew point prior to being fed into the heat exchanger, theformation of condensate on the surfaces of the heat exchanger can bepractically eliminated, thereby extending the useful life of the heatexchanger, burner and associated combustion components.

7 Claims, 4 Drawing Figures Cacx (Hear) BACKGROUND OF INVENTION Thisinvention relates generally to liquid heaters and more particularly tofeed injected heaters utilized for the purpose of preheating the liquidmedium being supplied to the liquid heating system.

The concept of preheating in some manner liquid feed to a liquid heatingsystem is not new. U.S. Pats. Nos. 2,574,368 (122-411); 3,260,245(122-451) and 3,131,676( 122-451) all disclose liquid heating systemswhere a portion of the liquid as heated or superheated in the heatexchanger is pumped from a separater back into the liquid feed linecarrying the liquid feed from the liquid supply source or tank to theheat exchanger via the action of a supply pump. Other liquid heatingsystems such as shown in U.S. Pats. Nos. 3,399,655 (122-406); 1,401,893;and 2,751,894 (122-448) employ preheat systems having a heat exchangecoil housed within a jacket or enclosure so that a heat exchange takesplace between the liquid flowing through the coil and the liquid flowingthrough the enclosure, with one of the liquid flows being the liquidfeed to the liquid heater. However, such a preheat system are generallynot the once-through type.

Another type of preheat is shown in US. Pats. Nos 144,937; 391,390;985,834; and 1,823,154, wherein a portion of the heated liquid from theliquid heater is directed back through a feed return to an injectionnozzle where it is commingled with colder liquidfeed and returned to theheat exchanger. In the case of U.S. Pat. No. 391,390, the nozzle formspart of the liquid feed supply producing a siphon or suction to drawthereinto already heated liquid being drawn from the feedback lineconnected to a preheater within the main heating system. These patents,in general, recognize that preheating can help to eliminate the effectsof cold water or liquid on heated surfaces or pitting caused by lowtemperature liquid mediums.

However, none of these systems for preheating are concerned with theproblem predominently present here wherein a large amount of condensateis formed in the heater due to the application of a colder temper atureliquid medium being presented to high temperature heat source whereinthe liquid heater system is of the once throughT type, i.e., the liquidheated medium is not intended to be returned to the heater orcirculatory in the heating system. If the temperature of liquid feedwere above the dew point of the liquid upon entering the heating system,the condensate would not be formed on the heater exchanger portions ofthe system. Condensate formed on the structural heater portions of aonce-through heating system, usually a heating coil, have been known todeteriorate and destroy the heating coil in a relatively short time dueto corrosive and chemical effects on the outside of the heating coil,particularly when the liquid entering the heating coil is at a lowtemperature, for example, at 40 F or less.

The type of heating system herein disclosed can be generallycharacterized as steam cleaner or pressure washer, the liquid system(the term liquid herein has reference to a solution of water andcleaning agent, but

principally water) which consists of a liquid source or supply, a pumpfor pumping the liquid feed, a heat exchanger in the form of a heatingcoil to heat to a high temperature the liquid feed to produce from theliquid a vapor spray within a latent heat zone for applying through anoutlet nozzle directly to the surface of an object to be washed orcleaned of dirt, foreign particles and other such matter. A large volumeof condensate is generated on the surfaces of heating coils of theseliquid systems in view of the fact that the liquid feed supplied to theheating coil is at a low temperature below the dew point. The condensatecontinually deposited on the heating coil over a period of time corrodesthe heating coil to a point where replacement is essential.

The condensate-coil problem is more pronounced on steam cleaners havingliquid heating systems employing natural gas, rather than liquid fuel,as the means for supplying heat through a burner to the heating coil ofthe cleaner. Natural gas, being a fossil fuel, has a large amount ofhydrogen present which, due to the act of combustion at the burner, isreduced to H O by the equation OH, 20 CO 2H O. This water as a vaporpasses with the flue gases by the heating coil. The heating coilsurfaces being at a lower temperature, cause the vapor to condense onthe heating coil surfaces and accumulate to a point where the condensatewill continually drip and drain from the heating coil. Over a period oftime, this condensate will corrode the heating coil and the dripping anddraining of the condensate will corrode the steam cleaner or pressurewasher enclosure. Also, the condensate being formed will reduce theefficiency of operation of the heat exchanger. Thus, if the temperaturesin the combustion and heat exchange area, or in the case here, theheating coil per so, were above the dew point of the liquid at theoperating atmospheric conditions, the water formed as a by-product ofcombustion would pass off as water vapor and would not form on theheating coil as condensate.

In this type of system, it is conceivable that a preheating arrangementcould be employed by taking a portion of the heated liquid medium fromthe outlet of the heating coil and feeding it back directly to theliquid source or supply, such as a tank, so that the incoming liquidwould be commingled with a portion of the feedback heated liquid.However, such a system, although it would undoubtedly help preventcondensate from forming on the heating coils, is not desirable due tothe noise created and the superheated liquid flashing to steam whenexposed to the ambient atmosphere at liquid supply tank. This problemwas recognized in U.S. Pat. No. 3,260,245. Furthermore, the capacity ofheat liquid output of the system would be reduced.

To eliminate flashing, the feedback of a portion of the heated liquidcould be directed to a point in the liquid feed line between the liquidsupply pump and the liquid supply tank. Although the condensate .couldbe prevented from forming on the heating coil and flashing could beminimized, the higher temperatures on the pump parts, such as the inletand outlet check valves, has a detrimental effect by reducing theefficiency of the pump as well asinterfering with pumping, as pulsationscaused by pumping the liquid feed in the first instance would also beapplied at the inlet check valve side or suction side of the liquidsupply pump. Also, vapor lock could becreated on the suction side of thepump as recognized in U.S. Pat. No. 3,260,245, and the output orcapacity of the liquid heating system would be reduced.

We have found that the best point of return of a portion of the heatedliquid as a feedback in a pre-heat system of the type herein disclosedis its insertion into the liquid feed line between the outlet valve sideor pressure side of the liquid supply pump and the heating coil of theliquid heating system. However, being the high pressure, output side ofthe liquid displacement pump, it is difficult if not impossible toinsert a feedback liquid into a pressure line having a greater pressurethan the pressure in the feedback line. We have conceived that byproperly employing a Venturi injector in the liquid feed line betweenthe outlet of the pump and the heating coil, a static pressure point canbe created so that the feedback line pressure is quite sufficient topermit the introduction of a portion of the already heated liquid intothe liquid feed being supplied to the heating coil to raise thetemperature of the latter above its dew point prior to being supplied tothe heat exchanger.

Although the Venturi concept is quite old, its employment as a preheaterin the steam cleaner or pressure washer art is not known, nor the manneras to how it can be properly employed to do an effective job ineliminating condensate from forming on a largev scale on the heatingcoil. The liquid heating system of U.S.

Pat; No. 2,800,117 does show the employment of a Venturi in a heatedliquid feedback line in combination with a differential pressure bypassvalve to provide operation of the latter when there is heated liquidbeing fed back to the system from a separator; but there is noemployment of the Venturi in this Patent as employed in thepresent'disclosure wherein the Venturi is in the supply line to theheating coil for the purpose of permitting the introduction of a portionof the already heated liquid from the heat exchanger into the liquidfeed supply to raise the temperature of the latter to the dew point.

SUMMARYOF THE INVENTION The principal object of the present invention isthe employment ofa Venturi injector in the liquid feed line between theliquid feed pump and the heat exchanger or heating coil in a liquidheating system, such as a steam cleaner or pressure washer, particularlywhere the liquid heating system is of the once-through type. Inemploying a Venturi in this point in the liquidfeed supply, the energynecessary to introduce already heated liquid into the feed supply lineto the heating coil from a lower pressure point at the coil outlet to ahigher pressure point in the feed supply line from the pressure side ofthe feed supply pump comes from the development of a pressure drop atthe narrow point of the Venturi injector.

The total capacity or output of the system is not effected, since thereturn or feedback of a portion of the heated liquid is returned intothe system on the pressure side of the liquid feed pump rather than tothe liquid supply tank or the suction side of the feed pump. Of course,additional higher pump pressures are required, meaning more drivingpower, due to the restriction imposed upon the feed pump by theinsertion of the Venturi injector in the feed supply line to the heatingcoil. However, it has been found that the Venturi injector is veryeffective in eliminating condensate from forming on the surfaces of theheating coil, particularly in connection with those steam cleaners orpressure washers using natural gas as the combustible fuel at theburner, though it is equally effective with other fuels, forming H O asone of the products of combustion.

Another object of the present invention is the employment of a Venturiinjector as preheater feedback system in a once-through'steam cleaner orother such liquid heating system increasing the life expectancy of theheating coil by several years, as well as protecting the chassis andcombustion chamber box of the steam cleaner from being continuallysubjected to dripping and draining condensate.

In normal service, although difficult to readily generalize, a heatingcoil will usually exceed 5 years of life before necessary replacement,but most heating coils do not reach 10 years of use. Thus, from apractical standpoint, most heating coils being defective and inoperativewith continuous and normal use between 5 to 10 years, i.e., a lifeexpectancy of 5 to 10 years. In natural gas operated steam cleaners usedused extreme atmospheric and cold liquid conditions such as around 40 Ftemperature liquid with the relative humidity at percent and temperatureat 95 F, the heating coil life can be reduced to three to 6 months lifeexpectancy.

with the employment of the Venturi injector of the present invention,the heating coil life expectancy can be increased several times,depending on atmospheric and liquid temperature conditions. In normalservice under general seasonal conditions found in the central andnorthern United States, the employment of the Venturi injector system insteam cleaners has been found to increase the heating coil life by atleast 2 years or more.

Another object of the present invention is the provision of a liquidheating feedback system in a steam cleaner to minimize condensate formedon the heating coil of the cleaner by returning or recirculatingsuperheated water from the outlet of the coil back to the inlet ofthecoil in the liquid feed supply line leading to the heating coil. Coldwater or liquid from the feed pump is pumped into the Venturiinjectorpositioned in the feed supply line. Because the narrow portionor the orifice of the Venturi injector creates a vacuum or reduced,pressure, in accordance with the well-known Bernoulli theory as appliedto Venturi devices, superheated liquid is drawn through the feedbackline from the heating coil outlet into the feed supply line to theheating coil. The injected liquid feedback is at a point in the Venturiinjector immediately after the point in the Venturis orifice where thepressure is minimal.

The superheated liquid at this point in the Venturi injector mixes withthe oncoming colder liquid supply from the feed pump to raise thetemperature of the colder liquid. As a result, the incoming liquid feedto the heating coil can be above its dew point temperature and the waterformed as a by-product of combustion, particularly in natural gas fuelsteam cleaners, or due to high humidity atmospheric conditions willleave the combustion chamber of the. steam cleaner as a vapor and notprecipitate out as a condensate on the surface of the heating coil,burner and associated components.

Other objects and advantages appear in the following description andclaims.

The accompanying drawings show, for the purpose of exemplificationwithout limiting the invention or the claims thereto, certain practicalembodiments illustrating the principles of this invention wherein:

FIG. 1 is a diagrammatic illustration of a combination steam cleaner andpressure washer employing a Venturi injector preheater forming a liquidheating feedback system for the steam cleaner.

FIG. 2 is a diagrammatic view of the hydraulic circuitry of the liquidheating system of a combination steam cleanerand pressure washeremploying the Venturi injector feedback system of the present invention.

FIG. 3 is a longitudinal cross-sectional view of the Venturi injectorcomprising this invention.

FIG. 4 is a diagrammatic view of the hydraulic circuitry of the liquidheating system of the steam cleaner to illustrate the temperature,pressure and volume relationships to determine the orifice size of theVenturi.

Reference is now made particularly to FIG. 1 which A diagrammaticallyillustrates a liquid heating system of the once-through" type andspecifically referred to as a combination steam cleaner and pressurewasher, but hereinafter referred to as steam cleaner 1.

The steam cleaner 1 is provided with a liquid heating feedback systemgenerally identified at 2 for redirecting a portion of the liquid feedfrom the outlet of the heating coil 3 back into the liquid feed beingsupplied to the heating coil.

In general, the steam cleaner 1 is provided with a liquid feed pump 4 ofthe duplex type consisting of the double ended piston 5 and the rightand left pumping chambers 6 and 6, respectively. The piston 5 is drivenor reciprocated by means ofthe rod 7 connected by the eccentric 10 tothe pulley 8. The pulley 8 is rotatably driven by means of the motor 11through the belt 12.

Motor 11 is connected to a suitable electrical source by means of line13 through the motor switch and power drop cord as indicated in FIG. 1.I

The respective outputs of the pumping chambers are provided with theaccumulators 14 to absorb the impulses created in pumping the liquid bymeans ofthe liquid feed pump 4 so that the final liquid supply output tovapor hose l5 and nozzle 16 is uniform rather than pulsating.

The output from the left side chamber 6 of the liquid feed pump 4 isconnected by conduit 17 directly to the vapor hose to bypass the heatexchanger and thus expand the flow range, to provide for a pressurewasher if so desired. In this connection, it is important to realizethat when the system is operated in the pressure washer mode, theby-pass conduit provides for reduced operating pressure at the pumpsince all liquid being pumped is not being applied along conduitl8through restricting injector 60 of the feedback system, which will beexplained later in greater detail. Moreover, the

temperature of the liquid will be maintained at a higher temperature ascompared to the all liquid supply provided by pump 4 through conduit 18.Thus, no matter what mode, whether a steam cleaner or a pressure washer,the apparatus is operating in, the same amount or volume of preheatedliquid feedback to the input of the heat exchanger will be needed toelevate the temperature of the liquid feed above the dew point. Said inother words, when the liquid heating system is being operated in thepressure washer mode, less volume of pre-heated liquid is required to befed back through the feedback system 2 than would be normally requiredif the entire output of the liquid feed pump were able to be applieddirectly to the heating coil 3.

On the other hand, the outlet supply of the right pumping chamber 6' ofthe liquid feed pump 4'is supplied through conduit 18 through the liquidheating feedback system 2 and thence .by conduit 20 to the inlet 21 ofthe heating coil 3. The outlet 22 of the heating coil 3 is connected bymeans of conduit 23 by connector 24 to conduit 17 and the vapor hose 15.A safety fuse plug 25 is provided to be connected to the fourwayconnector 24. Plug 25 has a central opening provided with a softmetallic material which will melt if the temperature of the liquidheated by the coil 3 is above a predetermined and undesirabletemperature. Thus, the safety fuse plug 25 provides an inexpensivesafety feature in preventing the temperature of the heating system fromexceeding a point where it would damage the liquid heating system,particularly the heating coil 3.

From the foregoing explanation, it can be seen that the liquid supplyprovided by the liquid feed pump 4 provides a pressure wash when bothconduits l7 and 18 are providing liquid to the vapor hose 15. When inthe pressure washer mode, it can be seen that one portion of the liquidprovided by pump 4 through pumping chamber 6 is heated while the otherportion is not, thereby maintaining a high temperature condition inheating coil 3, regardless of whether the apparatus is in the pressurewasher mode or not. Thus, the nozzle 16 can provide in this mode astream of heated water under high pressure for washing purposes.However, if the pressure washer mode is not desired, the liquid supplyprovided at the output of the left pump chamber 6, is cut off by meansof a control valve shown at 54, so that the entireliquid supply providedto the nozzle 16 is through conduit 18 and through the heating coil 3,thence through conduit 23, connector 24 and into vapor hose 15. As such,the liquid supply is superheated and under normal operating conditionshas an output temperature of approximately 325 F. Thus, a portion of thesuperheated liquid will flash into steam at nozzle 16.

The heat exchanger in the form of heating coil 3 is housed within aninsulated fire box generally indicated at 26, the bottom of which isprovided with a burner assembly 27. The burner assembly is provided withfuel, in this case, natural gas, by means of the conduit 30, the end 28of which is connected to a convenient source of natural gas fuel. Asshown in FIG. 1, the conduit 30 is provided with a main gas cock 3], apressure regulator 32 and a solenoid operated gas valve 33. The solenoidoperated gas valve 33 is operated in the usual manner as found in allgas operated devices wherein the burner assembly 27 is provided with thepilot 36, the flame of which is directed against the thermocouple 34 inorder that pilot switch 35, connected to thermocouple 34 by means of thelines 37, permits the solenoid gas valve 33 to supply gas to the burnerassembly 27. In this connection, pilot switch 35 is also electricallyconnected through burner switch 38 by means of the electrical supplyline 40 to a convenient electrical source or supply.

duit 44 into the water float tank 45 where it is commint The pilot 36 isalso connected through pilot switch 35 c indicated at 46 and is suppliedthrough conduit 47 through water float valve 48 into the water floattank 45. Water float valve 48 is provided with the tank float 50 andpermits water to enter the tank 45 until the float 50 has risen to apredetermined level, at which time, it will operate the water floatvalve 48 to cut off the water supply through conduit 47.

As previously mentioned, the commingling or mixing of the solution withthe water supply is termed as the liquid supply, which proceeds from theoutlet 51 of the tank 45 through the respective supply lines 52 and 53to the respective left and right pumping chambers 6 and 6' of the liquidfeed pump 4. It will be noted that conduit supply line 53 is providedwith the volume selector control valve 54 which can be opened to providefor the pressure washer mode or closed to provide the steam cleaner modeas previously explained.

It also should be noted that relief valve 55 is provided at the inlet 21of the heating coil 3 in conduit 20 as a safety feature so that if theheating coil should become clogged or theflow inside the heating coilotherwise becomes interrupted, the pressure in conduit 20 will exceedthe pressure setting ofrelief valve 55, thereby opening relief valve 55and permitting relief of the system by directing the liquid feed supplyback into the water float tank 45 by means of the conduit 56 as shown inH6. 1.

Reference now will be made in particular to the liquid heating feedbacksystem 2 comprisingthis invention. The liquid heating feedback system 2principally consists of the Venturi injector shown at 60 which isconnected direct-1y in the liquid feed supply lines to the heating coil3.. As shown, conduit 18 is connected to the inlet side of the injector60, whereas conduit 20 is connected to the outlet side of the injector60. The tee connections 57 are provided for the purpose of connectingbypass conduit 58 respectively to the inlet and outlet sides of theinjector system. Bypass conduit 58 is also provided with a relief valve61. The relief valve '61 in combination with the bypass conduit 58 is asafety feature so that if the injector 60 ever became obstructed orwould not permit the passage of fluid therethrough, the pressure reliefvalve. 61 would be caused to be opened to permit the passage of liquidaround and bypassing of the injector 60 by means of conduit 58.

The purpose of the Venturi injector 60 is to take a portion of theheated liquid from the output of the heating coil 3 and redirect it intothe liquid feed being supplied by the pump 4 to the inlet 21 of theheating coil 3. This feedback of a portion of the heated liquid isprovided by means of the feedback conduit 62 which is directed to thetank 45 through the water float valve 48 operated by float 50. Tank 45is provided with two outlets providing liquid to the pump 4 which hastwo pumping chambers 6 and 6. The pumping chamber 6 is connected byconduit 53 to the supply tank 45 through the volume selector controlvalve 54 and an inlet check valve 6a, whereas the other pumping chamber6 of pump 4 is connected by means of conduit 52 through an inlet checkvalve 60. The pumping chamber'6 isconnected through an outlet checkvalve 6b by means of conduit 17 directly to the hose and the spraynozzle 16. On the other hand, the outlet of has one end connected toconnector 24 of conduit 23 from the outlet 22 of the heating coil 3 andits other end connected to the tee member 63 of the injector 60, whichis also shown in H0. 3. The tee member 63 has its other or opposite endconnected to conduit 64 which is connected to pressure gage 65 in orderto readily determine the pressure of the heated liquid delivered tovapor hose 15. The location'of this pressure gage line 64 at tee member63 greatly reduced damaging pulsations at pressure gage 65.

Reference is now made to the fluid diagrammatic illustration of FIG. 2to summarize the foregoing description concerning steam cleaner 1 withemphasis particularly directed to the fluid heating system and supply.As shown in FIG. 2, the liquid feed supply 46 the other pumping chamber6 of pump 4 is supplied through an outlet check valve 6b through conduit18, thence through the Venturi injector 60, conduit 20 to heating coil 3and thence by conduit 23 connected to the output of heating coil 3 tothe hose 15. The feedback conduit 62 is connected at 24 in conduit 23directly to the injector 60 through a lateral passage, which will beexplained later. Bypass line 58 around the injector 60 is shownconnected with one end to conduit 18 with its other end connected toconduit 20 with relief valve 61 connected in bypass conduit 58.

Reference is now made specifically to FIG. 3 which illustrates in crosssection the structural features of the Venturi injector 60. The injector60 is provided with a cylindrical chamber 66 made up of threecylindrical sections 67, 68 and 70. The forwardmost section 70 isprovided with an axially aligned divergent outlet passage 71.1Passage 71 provides for communication between chamber 66 and conduit 20, which isconnected to the injector 60'by means of the threaded end 72. Outletpassage 71 is also of increasing diametrical extent from its innermostend indicated at 73 to its outermost end at 74. i

. Chamber 66, having chamber sections 68 and 70 of different diametricalextents, provides for the annular shoulder 75. Section 68 is adapted toreceive the nozzle 77. Converging nozzle 77 has a centrally locatedorifice 78 which has a diminishing diametrical extent from the inlet end80 to its outlet end 81 in the nozzle head 82. Thus, injector nozzles 77having different sized orifices may be press fitted into the chambersection 68 to meet the necessary requirements for an operative liquidheating feedback system. i

The threaded bore 76 is connected by suitable means to conduit 18.

The tee member 63 shown in FIG. 3 has a threaded end 84 connected toconduit 64 as shown in FIG. 1 whereas the threaded end 83 is connectedto the feedback conduit 62. Tee member 63 also is provided with eralpassage 85 of the in jector'60, which lateralpassage leads directly intothe chamber section 70 of the inje ctor'. Thus, the feedback heatedliquid is fed back through tee member 63, then lateral passage 85 intothe chamber section 70 within which is extended the nozzle head 82. I

The employment of the injector 60 is required in order to obtainadequate feedback of the heated liquid because the pressure of theliquid in the conduit 18 from the pump 4 is higher than the pressure ofthe liquid being returned through feedback conduit 62 By employinginjector 60, the pressure drop at chamber section 70 is nearly zero sothat the liquid pressure in the feedback conduit is sufficient to injectthe heated liquid into the feed supply from conduit 18. Thus, de-

pendent on the amount of feedback liquid necessary to raise thetemperature of the liquid supply above the dew point and the operatingpressures involved, the size of the orifice 78 can be predetermined andproperly selected.

Explanation now will be made in connection with FIG. 4 reqarding thesize of the outlet diameter 81 of the orifice 78 which is dependent uponinlet conditions of the liquid feed, that is, the volume, temperatureand pressure values of the inlet in relationship to the desired pressureand temperature conditions of the liquid feed as supplied directly tothe heating coil 3. Such a discussion must assume certain theoreticalconditions in order to arrive at a temperature at which the liquid feedlevel should be upon entrance of the heating coil 3 in order to preventthe formation of condensate on difference of the critical and incomingtemperature, T T,, to the difference in the bypass temperature and Ycritical temperature, T T

the surfaces of the coil. Assuming maximum condensation upon the mostextreme but possible atmospheric conditions, upon experiment andmathematical deduction, it can be calculated that the maximum requiredinlet temperature of the liquid feed at the inlet 21 of the heating coil3, Le, temperature T of FIG. 4, should be at least 145 F, assuming thatthe ambient temperature is 95 F and the relative humidity is 95 percent.However, under normal operating environment, these conditions are quiteextreme. For example, typical operating conditions would be as follows:ambient temperature 72 F with relative humidity at 58 percent. The inletliquid feed supply had a temperature level at 69 F. The desired outlettemperature, T,, would have to be approximately 325 F. In view of theseconditions, the inlet temperature to the coil, T should be 129 F toinsure almost complete elimination of condensate on the surfaces of theheating coil.

However, making reference again to the extreme conditions and to assurethat the proper temperature, T is reached, that is, 145 F, the rate offlow, O in feedback conduit 62 must be controlled. In order to determinethis flow rate, 0 the following values must be determined:

Q, the incoming flow as measured in cubic feet per second;

T the temperature ofthe liquid feed supply from pump 4;

T the temperature of the feedback liquid from the outlet of the heatingcoil 3 directed at point 24 into the feedback conduit '62, whichtemperature is equivalent to the output temperature of the heating coilitself;

T the critical temperature which must be achieved to eliminatecondensate by raising the temperature level of the liquid feed supplymoving through conduit to the heating coil 3, which, as previouslyindicated under extreme conditions must be at least 145 F.

By utilizing the heat balance equation in reference to FIG. 4:

T3Q3 lQl T2Q2 and .the fact, upon viewing FIG. 4, that QzF Q: Q2

therefore,

Q2 a l/ 2 a) Q1 Thus, the bypass flow rate is equivalent to the productof the incoming flow rate 0, times the ratio of the Having establishedthe bypass flow rate, Q which is dependent upon the incoming flow rate,Q,, the pressure head identified as 11 at the point of injection, thatis, at lateral passage in chamber section 70, can be calculated, knowingthe quantities for I1 which is the bypass line pressure head as measuredin feet, and d which is the diameter of the lateral passage 85.

The pressure head h is equal to the bypass pressure head, hg plus aconstant times the square of the ratio of the bypass flow rate to thebypass opening area. indicated as A by the following equation: 11,, 11QflA,

Since the pressure head h has been determined for a given incoming flowQ and the necessary bypass flow rate Q, can be readily calculated, theproper diameter D for the opening of the nozzle orifice 78 at theforward end 81 can be obtained by the following formula:

Solving the above equation to obtain D and applying the constants, thefollowing formula is obtained:

d D, I Q /(36.7 11,, D Q A Thus, from the foregoing formula for theproper diameter of the nozzle orifice 78 at 81, it can be seen that thesize in diameter is directly proportional to the flow rates 0, and Q2,the temperatures T, and T flow as the pressure value together with thediameter of the lateral passage identified at 85 in FIG. 3. Thus. inorder to insure the proper temperature level T at the inlet 21 of theheating coil 3, calculations can be made to determine the size of thenozzle orifice 78, knowing the temperature level T and the inlettemperature of the liquid feed, T including the flow rate, Q, and thediameter of the lateral passage 85.

We claim:

1. A liquid heating feedback system for elevating the temperature abovethe dew point of the liquid feed to a heat exchanger of a liquid heatingsystem to eliminate the formation of condensate on the surfaces of theheat exchanger comprising a heat exchanger consisting of a heatconducting conduit convolution exposed to ambient atmosphere for thepassage of a liquid therethrough to be heated and burner meanspositioned under said conduit convolution to heat the same and a liquidcontained therein, 7

a liquid feed source,

conduit means connecting said liquid feed source to said heat exchanger,

a feed pump connected in said conduit means for pumping liquid from saidsource to said heat exchanger,

a Venturi injector in said conduit means between said pump and said heatexchanger,

a discharge nozzle connected by second conduit means to the output ofsaid heat exchanger,

and third conduit means having one end connected to the output of saidheat exchanger and its other end connected to said Venturi injectorwhereby a portion of heated liquid from said heat exchanger output isfed back and commingled with the liquid feed being pumped to said heatexchanger.

2. The liquid heating system of claim 1 characterized in that saidVenturi injector includes a Venturi nozzle having a central orifice, alateral opening extending into said injector adjacent to said Venturinozzle, the size of said orifice dependent directly on the rate of flow,pressure and temperature of the liquid feed to said injector and thediameter of said lateral opening.

3. The liquid heating system of claim 1 characterized by a cylindricalchamber extending into said injector from its inlet side, a Venturinozzle in said chamber and having a head extending forwardly into saidchamber, a lateral passage extending into said chamber adjacent saidVenturi nozzle head, an orifice in said Venturi nozzle having acontinuously diminishing diameter into said head, and an outlet passageaxially aligned relative to said orifice and extending forwardly fromsaid chamber with increasing diametrical width.

4. The liquid heating system of claim 1 characterized by third conduitmeans having its ends connected into said first-mentioned conduit meansrespectively at the inlet and outlet of said injector and a relief valvepositioned in said third conduit means.

5. The liquid heating system of claim 1 characterized by bypass conduitmeans having one end connected to the output of said feed pump and itsother end connected to the output of said heat exchanger to direct aportion of said feed pump output around said heat exchanger to providefor a pressure washer mode in said system and concurrently reduce thevolume of preheated liquid required at said injector to elevate thetemperature of the liquid feed above the dew point.

6. A liquid heating feedback system for elevating the temperature abovethe dew point of the liquid feed to a once-through heat exchanger in asteam cleaner to eliminate the formation of condensate on the surfacesof the heating coil comprising a heating coil as a heat exchanger,

a liquid feed source,

a liquid feed pump,

a first conduit connecting said source with said a second conduitconnecting said pump to said heating coil,

a Venturi injector in said second conduit and having an inlet chamber, anozzle in said chamber and having a central orifice of diminishingdiameter, an outlet passage leading from the forward end of saidchamber, a lateral passage in said injector into said a chamber adjacentto said nozzle,

a third conduit connecting the outlet of said coil to a-steam cleanerspray nozzle,

a fourth conduit having one end connected to said coil outlet and itsother end connected to said injector lateral passage whereby a portionof heated liquid from said coil is fed back and commingled with theliquid feed being pumped by said pump to said coil.

7. The liquid heating system of claim 6 characterized by a bypassconduit having its ends connected respectively to said injector inletchamber and said outlet passage, a pressure relief valve in. saidconduit.

1. A liquid heating feedback system for elevating the temperature abovethe dew point of the liquid feed to a heat exchanger of a liquid heatingsystem to eliminate the formation of condensate on the surfaces of theheat exchanger comprising a heat exchanger consisting of a heatconducting conduit convolution exposed to ambient atmosphere for thepassage of a liquid therethrough to be heated and burner meanspositioned under said conduit convolution to heat the same and a liquidcontained therein, a liquid feed source, conduit means connecting saidliquid feed source to said heat exchanger, a feed pump connected in saidconduit means for pumping liquid from said source to said heatexchanger, a Venturi injector in said conduit means between said pumpand said heat exchanger, a discharge nozzle connected by second conduitmeans to the output of said heat exchanger, and third conduit meanshaving one end connected to the outpUt of said heat exchanger and itsother end connected to said Venturi injector whereby a portion of heatedliquid from said heat exchanger output is fed back and commingled withthe liquid feed being pumped to said heat exchanger.
 2. The liquidheating system of claim 1 characterized in that said Venturi injectorincludes a Venturi nozzle having a central orifice, a lateral openingextending into said injector adjacent to said Venturi nozzle, the sizeof said orifice dependent directly on the rate of flow, pressure andtemperature of the liquid feed to said injector and the diameter of saidlateral opening.
 3. The liquid heating system of claim 1 characterizedby a cylindrical chamber extending into said injector from its inletside, a Venturi nozzle in said chamber and having a head extendingforwardly into said chamber, a lateral passage extending into saidchamber adjacent said Venturi nozzle head, an orifice in said Venturinozzle having a continuously diminishing diameter into said head, and anoutlet passage axially aligned relative to said orifice and extendingforwardly from said chamber with increasing diametrical width.
 4. Theliquid heating system of claim 1 characterized by third conduit meanshaving its ends connected into said first-mentioned conduit meansrespectively at the inlet and outlet of said injector and a relief valvepositioned in said third conduit means.
 5. The liquid heating system ofclaim 1 characterized by bypass conduit means having one end connectedto the output of said feed pump and its other end connected to theoutput of said heat exchanger to direct a portion of said feed pumpoutput around said heat exchanger to provide for a pressure washer modein said system and concurrently reduce the volume of preheated liquidrequired at said injector to elevate the temperature of the liquid feedabove the dew point.
 6. A liquid heating feedback system for elevatingthe temperature above the dew point of the liquid feed to a''''once-through'''' heat exchanger in a steam cleaner to eliminate theformation of condensate on the surfaces of the heating coil comprising aheating coil as a heat exchanger, a liquid feed source, a liquid feedpump, a first conduit connecting said source with said pump, a secondconduit connecting said pump to said heating coil, a Venturi injector insaid second conduit and having an inlet chamber, a nozzle in saidchamber and having a central orifice of diminishing diameter, an outletpassage leading from the forward end of said chamber, a lateral passagein said injector into said chamber adjacent to said nozzle, a thirdconduit connecting the outlet of said coil to a steam cleaner spraynozzle, a fourth conduit having one end connected to said coil outletand its other end connected to said injector lateral passage whereby aportion of heated liquid from said coil is fed back and commingled withthe liquid feed being pumped by said pump to said coil.
 7. The liquidheating system of claim 6 characterized by a bypass conduit having itsends connected respectively to said injector inlet chamber and saidoutlet passage, a pressure relief valve in said conduit.